A NSW Rural Fire Service report into a Blue Mountains bushfire that destroyed several homes does not mention the blaze was accidentally sparked by backburning, an inquiry has been told.
The long-running Black Summer bushfires inquiry was told an investigation report described the December 2019 Grose Valley fire, at Mount Wilson, as a "continuation" of the enormous Gospers Mountain fire.
Counsel assisting Donna Ward SC asked RFS witnesses if the report should instead acknowledge the fire was an unintended result of a "spot over" from backburning, designed to protect the surrounding villages.
"As the backburning was being undertaken for suppression of the Gospers Mountain fire, it would be deemed as part of the Gospers Mountain fire," RFS fire investigation training coordinator Mark Fullagar said on Tuesday.
"But the report probably should have said there were backburning operations undertaken."
Mr Fullagar and RFS Assistant Commissioner Ben Millington agreed readers of the report should have an accurate understanding of both the backburning and the "spot over".
Detective Sergeant Laura Harvey, the officer in charge of the Grose Valley fire case, said she requested a cause and origin investigation near the Bells Line of Road.
One month later, she discovered it had instead taken place at the Grose River to understand how the fire moved between two council areas.
Det Sgt Harvey said she was frustrated by the change of location.
"It's not helpful as to the cause and origin of the fire," she told the Coroners Court in Lidcombe.
Firefighting resources were so stretched during the 2019-20 season that only 10 out of 130 fire investigators were available at any one time.
"Considering the season we had, it didn't surprise us," Mr Fullagar said.
"Just the amount of fire that was on the ground and staff and volunteers being used in other roles."
There are now fewer bushfire investigators - 60 RFS volunteers and 46 staff - due to retirements and potentially COVID-19.
The inquiry was also told police were confused by the RFS convention to change the name of a fire as it crossed council boundaries.
NSW Police suggested fires should keep their original names followed by a number.
Mr Millington disagreed with the idea.
"That runs the risk of confusion and takes away from local understanding, particularly where we see large-scale fires burning 100 kilometres apart.
"Research post-fires shows community understanding of those references is optimal."
The inquiry continues before Deputy State Coroner Teresa O'Sullivan.
